Foreign Minister Jose Manuel Albares said Spain would not allow its military bases, which are jointly operated by the US and Spain but under Spanish sovereignty, to be used for attacks on Iran, which Spain has condemned, calling it "an unjustified and dangerous military intervention that is outside of international law."

Fifteen US aircraft have left the Rota and Moron military bases in southern Spain since the US and Israel launched weekend attacks on Iran, maps by flight tracking website FlightRadar24 showed on Monday. At least seven of the aircraft were shown on FlightRadar24as having landed at Ramstein Air Base in Germany.

The UK had also initially refused to allow the use of its bases for an attack on Iran, but on Sunday Prime Minister Keir Starmer authorized their use for "collective self-defense."

Spain's stance and the emphatic condemnation of the US-Israeli actions in Iran by Socialist Prime Minister Pedro Sanchez once again make it an outlier in the region, potentially straining its relationship with Washington further.

"Spanish bases are not being used for this operation, and they will not be used for anything not included in the agreement with the United States or for anything that is not in accordance with the Charter of the United Nations," Albares said, speaking to Spanish broadcaster Telecinco.

"The Spanish government will not authorize the use of the bases for anything beyond the agreement or inconsistent with the United Nations," he said, referring to Naval Base Rota and Moron Air Base.

Defense Minister Margarita Robles said the aircraft – primarily aerial refueling tankers including the Boeing KC-135 "Stratotanker" – had been permanently stationed in Spain.

FlightRadar24's tracking website showed nine tankers departed on Sunday from the Moron airbase in southern Spain and headed towards Germany.

Two flights departed from Rota, a naval base with an airfield, towards southern France, the flight tracking website showed. A further four flights departed from Rota but their route was not shown.